WO2014032615A1

WO2014032615A1 - Portable metal ion detector

Info

Publication number: WO2014032615A1
Application number: PCT/CN2013/082690
Authority: WO
Inventors: Diana BAO
Original assignee: Bao Diana
Priority date: 2012-08-31
Filing date: 2013-08-30
Publication date: 2014-03-06
Also published as: CN104995499A

Abstract

A portable metal ion detector (100) includes high sensitivity and high selectivity through the use of a fluorescent molecule that selectively binds to metal ions such as Hg²⁺. The portable detector (100) correlates the fluorescence intensity of a sample to the amount of metal ion in the sample using one or more reference standards. The portable detector (100) can be used at or near the site where sample collection occurs and provide immediate or near immediate results.

Description

PORTABLE METAL ION DETECTOR

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The invention is generally in the field of portable metal ion detectors.

2. Related Technology

[0002] Hg²⁺ is a highly toxic metal ion that causes serious health and environmental problems. Increasingly, governments are recognizing the need to monitor and regulate the amount of Hg²⁺ released into the environment. Acceptable concentrations of Hg²⁺ are quite low. For example, in order to provide safe drinking water, Hg²⁺ levels should be less than 2 ppb (or 10 nM).

[0003] To detect such trace amounts of Hg²⁺ with minimal false positives, a sensor technique with extremely high selectivity is needed. Achieving selectivity can be very difficult because Hg²⁺ ions co-occur in nature with other physiologically important divalent metal ions such as Mg²⁺, Mn²⁺, Ca²⁺, Zn ⁺, Fe²⁺ and Cu²⁺. Moreover, contaminated water samples may include Cd²⁺, Pb²⁺, Ba²⁺, Ni²⁺ and other ions, the presence of which may be detrimental to human health. In addition, the concentration of these other ions may be much higher than that of Hg²⁺, which presents a significant challenge to accurately detecting the Hg²⁺ concentration.

[0004] Devices that provide high sensitivity and selectivity for Hg²⁺ detection are known. However, these devices are large, expensive, and not portable. Thus, the sample has to be prepared and delivered to the apparatus for detection. This approach creates problems with sample handling and increases processing costs. Portability is highly advantageous because of the need to detect Hg²⁺ in remote and/or varied locations. Portable systems significantly reduce sample handling and can provide results in the field in real time. The need for portability has led to a number of hand held devices for Hg²⁺ detection. For example, some existing handheld devices scan for the presence of Hg²⁺ using UV absorption techniques. However, despite great efforts, the industry has failed to produce a cost effective hand held device with the sensitivity and selectivity needed for properly monitoring Hg²⁺.

BRIEF SUMMARY

[0005] The present invention relates to a portable metal ion detector system with high sensitivity and selectivity. In one embodiment, the metal ion is Hg²⁺. The portable detector system correlates the fluorescence intensity of a sample to the amount of metal ion in the sample using one or more reference standards. The detector system can be used at or near the site where sample collection occurs and provide immediate or near immediate results.

[0006] In one embodiment, the metal ion detector system includes a housing that at least partially encloses a sample chamber, a light source, a fluorescence detector, and electrical circuitry. The sample chamber is configured to hold a sample that includes a metal ion such as, for example, Hg²⁺. The light source is optically coupled to the sample chamber and illuminates the sample. The light source has a wavelength suitable for excitation of a mercury-binding fluorophore. The emission wavelength of the fluorophore is selectively sensitive to binding with the metal ion. Upon binding with the metal ion, the fluorophore changes in fluorescence. In one embodiment, the change in fluorescence can be any detectable change in emission that correlates to Hg²⁺ binding. For example, Hg²⁺ binding can decrease fluorescence intensity, increase fluorescence intensity, or shift the fluorescence wavelength.

[0007] The fluorescence intensity of the test sample at a particular wavelength as compared to a reference standard is indicative of the concentration of metal ion in the sample. The fluorescence intensity at a particular wavelength is detected using a fluorescence detector optically coupled to the sample chamber. Electrical circuitry correlates the fluorescence intensity of the test sample with fluorescence intensity of a reference sample with a known metal ion concentration. For example, the concentration of Hg²⁺ in the reference sample that produces the same fluorescence intensity as the test

2+

sample is indicative of the concentration of Hg in the test sample.

[0008] To calibrate the device one or more reference standards with known metal ion concentrations are placed in the device and the fluorescence is measured and stored. By using a plurality of reference standards with different known concentrations of metal ion, a relationship between fluorescence intensity and metal ion concentration is established and stored in the electrical circuitry of the device. This relationship allows accurate correlations of metal ion concentrations at concentrations that are in the range of, but not the same as the concentrations of the reference standard. To achieve the most accurate correlations, it is desirable to calibrate the device using reference standards having a metal ion concentration that spans the estimated concentration of metal ion in the test sample.

[0009] These and other advantages and features of the invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] To further clarify the above and other advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. It is appreciated that these drawings depict only illustrated embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:

[0011] Figure 1 is a schematic of a portable mercury detector device according to one embodiment of the invention;

[0012] Figure 2 is a perspective view of a portable mercury detector;

[0013] Figure 3 is a perspective view of the portable mercury detector of Figure 2 with the sample cover open to reveal the sample chamber;

[0014] Figure 4 is a titration curve of a solution of 1 μΜ fluorophore;

[0015] Figure 5 is a linear fit of a portion of the titration curve of Figure 4;

[0016] Figure 6 is a linear fit of a portion of the titration curve of Figure 7;

[0017] Figure 7 is a titration curve of a solution of 2 μΜ fluorophore; and

[0018] Figure 8 is a portable mercury detector device connected to a portable electronic device.

DETAILED DESCRIPTION

I. Portable Metal Ion Detector

[0019] Figure 1 shows a schematic representation of the optical and electrical configuration of a portable mercury detector 100 according to one embodiment of the invention. Portable mercury detector 100 includes an optical system 110 and electrical circuitry 1 12. Optical system 1 10 is configured to illuminate and sense a fluorophore in a sample and electrical circuitry 1 12 is configured to operate optical system 1 10 and correlate detection signals with a mercury concentration.

[0020] Optical system 1 10 may include a light source 1 14, pre-sample optics 1 16, a sample chamber 1 18, post-sample optics 120, and a detector 122.

[0021] The light source 114 may be any light source suitable for producing sufficient light at an excitation wavelength of the fluorophore to cause a detectable amount of fluorescence. The light source 1 14 may be a full spectrum light that is filtered to produce a desired wavelength suited for exciting the fluorophore or preferably the light source 1 14 may have an emission profile that is primarily at the excitation wavelength of the fluorophore. The light source may emit in the deep UV, UV, or visible regions.

[0022] The light source 1 14 is preferably a light emitting diode. Light emitting diodes are preferred for their efficiency, which is important to preserve battery life. LEDs tend to emit light in a narrow band of wavelengths, which may be selected to overlap in part with the excitation wavelength of the fluorophore. The LED can have a narrow emission width. For example, greater than 90% of the emission spectrum may be within a width of 20 nm. Although not required the LED may be a laser diode.

[0023] The mercury detector 100 may optionally include pre-sample optics 1 16. Optics 1 16 may be used to filter, transmit, and/or focus the light from light source 114. Pre- sample optics 116 may include any number of filters, mirrors, lenses, optical fibers, collimators, and the like to facilitate illumination of the fluorophore at the desired wavelength. Optics 1 16 preferably includes an optical filter that filters wavelengths above the excitation wavelength of the fluorophore and in particular wavelengths in the range of the emissions wavelength of the fluorophore used with detector 100. In general, emissions wavelengths are longer wavelengths than excitation wavelengths. Thus, the pre-sample optics may include a short-pass filter (i.e., allows shorter wavelengths). In one embodiment, the short pass filter may have a cutoff at about 380 nm, 488, nm, or 510 nm or within a range of plus or minus 20 nm of the foregoing wavelengths.

[0024] Sample chamber 1 18 is configured to receive and hold a sample and is optically coupled to light source 114. Sample chamber 1 18 may have a size suitable for producing a fluorescence intensity above the sensitivity of detector 122, thereby minimizing noise. The sample volume of sample chamber may be 0.1 ml - 10 ml, 0.3 ml - 6 ml, or 1 ml - 3 ml.

[0025] The sample chamber is made from a material that is translucent to the excitation and emissions wavelengths of the fluorophore. For example, the sample chamber may be a fused silica. In some embodiments the excitation and emissions wavelengths of the fluorophore may be in the visible spectrum and the sample chamber may be made from relatively inexpensive polymeric material. Examples of materials include fused silica, borosilicate glass, quartz, polystyrene, polycarbonate, or polypropylene.

[0026] The mercury detector 100 may also include post-sample optics 120 that optically couples light from the sample chamber to the detector 122. Optics 120 may be used to filter, transmit, and/or focus the light from sample chamber 118 in preparation of impingement of the light on detector 122. Post-sample optics 120 may include any number of filters, mirrors, lenses, optical fibers, collimators, and the like to facilitate illumination of detector 122. Optics 120 preferably includes an optical filter that filters wavelengths below the emissions wavelength of the fluorophore used with detector 100 (i.e., the detection wavelength). Thus, post-sample optics 120 may include a long-pass filter (i.e., allows longer wavelengths). In one embodiment, the long-pass filter may have a cutoff off that is at least 5, 10, 20, or 30 nm below the peak detection wavelength (i.e., peak emission wavelength of the fluorophore) and at least 5, 10, 20, or 30 nm above the emission wavelength of the LED.

[0027] The detector 122 is optically coupled to the sample chamber 1 18 and is configured to detect light within the emission wavelength range of the fluorophore. The detector 122 may be a photodiode, a photomultiplier tube, or a camera sensor such as a CCD sensor. The detector quantifies the amount of fluorescence emitted from the sample chamber 1 18. The quantity of light emitted correlates to the concentration of mercury in the sample. The detector 122 is preferably not in the direct path of light emitted from light source 114. This can be accomplished for example by placing the detector at an angle to the sample relative to the light source 114. The angle is preferably at least 90 degrees.

[0028] Electrical circuitry 112 is configured to receive an intensity signal from the fluorescence detector and correlate the intensity signal to a mercury concentration in a sample within the sample chamber and output the mercury concentration to a user interface. Electrical circuitry 1 12 includes electrical circuits and computer executable instructions for powering light source 114 and detector 122 and for storing and processing signals from detector 122 and displaying or communicating detection results to a user interface or a separate electronic device (e.g., a portable smartphone or tablet computer).

[0029] Electrical circuitry 122 includes a battery 124 that allows device 100 to be operated (i.e., sample data collected) in a portable manner (i.e., without a requisite power cord attached to a plug). Device 100 may include a power cord for charging battery 124 or temporarily operating device 100, so long as portable operation is possible.

[0030] The portable mercury detector is configured for portable use by using components that are relatively compact and energy efficient. For example, the power draw of the portable electronic device during use may be less than 50, 20, 10, 5, or 1 watts/hour. In one embodiment, the device may operate (i.e., scan samples and display or transmit the results) using 1 - 10, 1.5 volt batteries or a rechargeable battery of similar capacity. In an alternative embodiment, the number of 1.5 volt batteries (e.g., AA or AAA batteries) may be 2 - 6 or 3 - 4, or a rechargeable battery (e.g., Li ion or NiMH) of the same or similar capacity. This is substantially lower power draw than traditional fluorescence detectors. In one embodiment, the device is a handheld device, (i.e., a device small enough that a person can perform a scan of a test sample while holding the device in one hand).

[0031] Electrical circuitry 122 may include any number of ancillary components that provide time, location, and/or environmental parameters. Electrical circuitry and associated computer executable instruction may "stamp" or associate a current time and/or location of the test results of a particular sample collected and tested.

[0032] Examples of ancillary components that can be included are devices for providing a geolocation, such as a GPS unit or a WiFi radio that identifies SSIDs of wireless routers with a known geolocation. The electrical circuitry may include a thermistor to determine temperature of the ambient area where the sample was taken or to measure the temperature of the sample as it is being tested, a camera to take a picture or video of the scenery where the sample was taken.

[0033] The data produced from ancillary electrical components may be automatically or manually associated with results of a test sample. For example, the temperature, video or picture file, or geolocation may be associated with the results for a particular test sample and displayed to the user on an LCD screen or transmitted to a separate electronic device with the concentration readings for the particular test sample.

[0034] In one embodiment, the electrical circuitry may store a date and/or time from when the last calibration procedure was performed (which is described in more detail below). The date or time of last calibration may also be associated with the test results of a particular sample.

[0035] Electrical circuitry may also include a wireless radio for transmitting data, including data from ancillary components and/or fluorescence data and/or mercury concentration. The wireless radio may be used to transmit data to a separate electronic device and/or for receiving control instructions from another electronic device (i.e., to control the operation of device 100). The foregoing data may also be transmitted to a separate portable electronic device through a hardwire data connection.

[0036] Figure 2 illustrates a device 200 that includes optical and electrical components as described above with respect to Figure 1. Device 200 includes a housing 226 that at least partially encloses light source 1 14, sample chamber 1 18, fluorescence detector 122, and electrical circuitry 1 12. [0037] Housing 226 includes an LCD display 228, four operating buttons 230a, 230b, 230c, and 230d (collectively buttons 230), a sample chamber lid 232, and a data communications port 234, which can also serve as a power connector.

[0038] Housing 226, LCD 228, and buttons 230 are sufficiently compact that a person can easily transport device 200 by hand while walking outdoors (e.g., to a water source or potential contamination site). In one embodiment, housing 226 is sufficiently compact that a person can operate buttons 230 with one hand while supporting device 200 with the other hand. In one embodiment, the maximum length is less than 18, 12, or 8 inches and the width is less than 14, 10, or 6 inches.

[0039] Figure 3 illustrates the detector 200 with lid 232 in the open position to reveal sample chamber 218. Sample chamber 218 is sized and configured to receive a cuvette.

[0040] LCD 228 and buttons 230 are configured to display information to a user and receive input from a user, respectively. For example, LCD 228 and buttons 230 can be used to receive instructions and select options when calibrating device 200, measuring the mercury in a sample, and/or outputting or displaying test sample results. LCD 228 and buttons 230 may be electrically coupled to electrical circuitry 112 described above.

[0041] In a preferred embodiment, the battery of electrical circuitry 1 12 is disposed within housing 226 and provides a power source for light source 1 14, fluorescence detector 122, electrical circuitry 1 12 and LCD 228.

[0042] Optionally electrical circuitry device 200 may include a data connector 234 that is electrically coupled to electrical circuitry 112. II. Fluorophore

[0043] The fluorescent fluorophore can be any molecule that when combined with a sample that includes the metal ion will selectively bind to the metal ion. For example, a compound having the structure (I) is selective for binding Hg²⁺:

(I)

as described in Che et al. (2008) Chem. Comm. 12: 1413-1415.

Calibration of Portable Electronic Device

[0044] The portable metal ion detector includes electrical circuitry (including computer executable instructions) that is configured to measure the intensity signal of a test sample by comparing a fluorescence reading from the sample to a reference standard. This is typically accomplished by establishing a calibration curve for a particular fluorophore at a particular concentration.

[0045] The calibration curve can be established by making two or more fluorescent measurements at two or more different concentrations of metal ion {e.g., Hg²⁺). Typically, the measurements will include one reference standard with no metal ion (e.g., a blank with water) and a second reference standard with a known concentration of metal ion. Additional reference standards with known concentrations of metal ion may also be used. [0046] In one embodiment, for a given concentration of fluorophore, the calibration curve will tend to have a range in which a Hg²⁺ reading will be linear. Figure 4 shows a titration of a water solution of a thymine-based fluorophore at a concentration of 1 μΜ. As can be seen from the graph, linearity is quite good out to about 60 ppb Hg²⁺. Figure 5 shows a linear fit for the portion of the titration curve of Figure 4 between 0-60 ppb Hg²⁺.

[0047] In one embodiment, to calibrate device 200 to detect Hg²⁺ using a reference standard with the foregoing fluorophore at 1 μΜ, a first fluorescence reading is obtained using a blank water sample, i.e., in the absence of Hg²⁺. The fluorescence thus measured corresponds to the point at zero concentration of Hg²⁺ in the plot of Figure 5. A second fluorescence reading is obtained using a reference standard sample containing both 1 μΜ concentration of the fluorophore and known concentration of Hg²⁺ that is within the linear range as determined for the fluorophore (e.g., 50 ppb for the particular fluorophore illustrated in Figure 4 and 5). The fluorescence of the reference standard at 50 ppb of Hg²⁺ and the fluorescence of the blank sample form the two data points needed to make a line that should match the same linearity as plotted in Figure 5. Using the line the concentration of Hg²⁺ of an unknown sample can be calculated from the the fluorescence reading that yields a Hg²⁺ concentration between 0 and 60 ppb.

[0048] The calibration curve using two data points is a simple line. The line can be calculated according to the equation Y=KC + B where Y is the fluorescence intensity, C is Hg²⁺ concentration and K is the slope of the linear fit of the titration curve as illustrated in Figure 5.

[0049] Figures 6 and 7 illustrate how the linear portion of the titration curve can be extended to high concentrations by using a higher concentration of the fluorophore. Figure 6 shows a titration curve for the same fluorophore as in Figure 4, but at a concentration of 2 μΜ. The linear portion of the titration curve is between about 0-120 ppb Hg²⁺. Figure 7 illustrates a linear fit for the fluorophore at a concentration of 2 μΜ for Hg²⁺ concentration between 0 and 120 ppb. As can be seen, device 200 can be calibrated to take measurements at higher or lower concentrations of Hg²⁺ using an appropriate concentration of fluorophore and an appropriately selected reference standard of known Hg²⁺ concentration that spans a concentration range expected for the unknown sample.

[0050] In one embodiment, device 200 is calibrated for two or more different concentrations. The calibration calculations can be stored in electrical circuitry and used to calculate Hg²⁺ in test samples that have unknown concentrations of Hg²⁺. The electrical circuitry can be configured to store and use at least two calibration curves or at least three calibration curves. In one embodiment, the two or three calibration curves span a range on the order of 0- 10 ppb, 0-100 ppb, and/or 0-1000 ppb. In one embodiment, the portable mercury detector system includes at least two calibration curves for a first mercury concentration range that extends at or below 10 ppb and a second concentration range that extends above 10 ppb, respectively. In a second embodiment, the portable mercury detector system includes two calibration curves for a first mercury concentration range that extends at or below 50 ppb and a second concentration range that extends above 50 ppb, respectively.

III. Methods of Use

[0051] The present invention extends to methods of using the devices described herein to determine a metal ion concentration in a test sample. In one embodiment, the method includes (i) placing a test sample and an amount of the mercury-binding fluorophore in the sample chamber of the mercury detector and (ii) detecting the concentration of mercury in the test sample.

[0052] In one embodiment, the test sample may be any test sample suspected of containing Hg²⁺. In another embodiment, the test sample may include an aqueous sample, a mixed aqueous sample, a non-aqueous sample, hydrocarbons, a stack gas extract, and/or waste water from a processing stream.

[0053] In one embodiment, the test sample may also be pretreated with an oxidizing agent prior to being tested for Hg²⁺. Oxidizing the sample will produce Hg²⁺ ions from metallic Hg metal or organic mercury compounds. Subsequent to oxidation following

2+

protocols known to skilled artisans, the neutralized sample containing Hg ions is then analyzed using the portable mercury detector and the fluorescence detection system described herein.

[0054] The sample is typically collected as a bulk sample. A measured quantity of the bulk sample is combined with a measure quantity of fluorophore to create a known concentration of fluorophore in the sample. This known concentration of fluorophore should be the same concentration as the concentration of fluorophore used in calibrating the device.

[0055] The combined fluorophore and sample are typically placed in a cuvette and inserted into the sample chamber 118 of device 200 and the lid 232 closed to block out ambient light. Device 200 is then caused to scan the sample using optics 1 10.

[0056] The test samples may be collected on-site and/or in the field. The site may be a remote site with no utilities available from a municipality. The Hg²⁺ measurement can be taken on site to ensure minimal disruption of the sample and to avoid the need to package the sample for transport in a vehicle. [0057] Ancillary data such as time, location, temperature, and/or pH can be obtained at the site and associated with the test results of the sample (i.e., using the electrical circuitry of the device) alone or in combination with a separate electronic device.

IV. Separate Electronic Devices

[0058] Figure 8 illustrates a separate electronic device 800 that can be used in combination with device 200. Separate device 800 and mercury detector 200 may be connected using a wire 810 or alternatively may be electrically connected through a wireless radio capable of transmitting data (e.g., WiFi or Bluetooth).

[0059] In one embodiment, device 800 is a portable computing device such as a smartphone, tablet computer, or mobile PC. The mercury device can transmit test results or ancillary data to separate device 800 and/or separate device 800 may be used to collect ancillary data and associate the ancillary data with the test sample results/data. In a preferred embodiment, the ancillary data collected by the separate electronic device is associated with the test results/data from the device 200 in the same location as the sample is taken and/or scanned for mercury. This allows the user to have real time results and take another sample if needed while still at the site of sample collection.

[0060] The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims

What is claimed is: CLAIMS

1. A portable mercury detector system comprising:

a sample chamber configured to hold a sample;

a light source optically coupled to the sample chamber, the light source having an emission wavelength suitable for excitation of a mercury-binding fluorophore;

a fluorescence detector optically coupled to the sample chamber so as to receive fluorescent light generated in the sample chamber by the mercury- binding fluorophore;

electrical circuitry configured to receive an intensity signal from the fluorescence detector and correlate the intensity signal to a mercury concentration in a sample within the sample chamber and output a test result including the mercury concentration to a user interface; and

a housing that at least partially encloses the light source, sample chamber, fluorescence detector, and electrical circuitry.

2. The portable mercury detector system as in claim 1, wherein the electrical circuitry is configured to calibrate the intensity signal of the fluorescence detector based on one or more reference standards.

3. The portable mercury detector system as in claim 2, wherein the calibration is based on one or more reference standards including a thymine containing fluorophore.

4. The portable mercury detector system as in claim 2, wherein the calibration is based on an aqueous reference standard.

5. The portable mercury detector system as in claim 1, wherein the calibration is performed for at least two different ranges of mercury concentration.

6. The portable mercury detector system as in claim 5, wherein a first mercury concentration range extends at or below 10 ppb and a second concentration range extends above 10 ppb.

7. The portable mercury detector system as in claim 1 , wherein a decrease in fluorescence correlates with an increase in mercury concentration.

8. The portable mercury detector system as in claim 1 , wherein the user interface is integrated into the housing.

9. The portable mercury detector as in claim 1, comprising a battery disposed within the housing and providing a power source for the light source, fluorescence detector, and electrical circuitry.

10. The portable mercury detector system as in claim 1, wherein the user interface is integrated into a separate electronic device and the electrical circuitry is configured to output the mercury concentration to the separate electronic device.

1 1. The portable mercury detector system as in claim 9, further comprising an electrical connector integrated into the housing of the portable mercury detector, the connector providing a wired connection to transmit the mercury concentration to the separate electronic device.

12. The portable mercury detector system as in claim 9 further comprising a wireless radio within the housing of the portable mercury detector that provides a wireless connection to transmit the mercury concentration to the separate electronic device.

13. The portable mercury detector system as in claim 9, wherein the separate electronic device is a smartphone or a tablet computer, or portable computer.

14. The portable mercury detector system as in claim 1 further comprising a geolocator unit that determines the geolocation of the portable mercury detector at a particular site and associates the geolocation with one or more test results from samples taken at the particular site.

15. The portable mercury detector system as in claim 1 , wherein the light source illuminates the sample chamber at a wavelength in the UV or visible spectrum.

16. The portable mercury detector system as in claim 1 , wherein the fluorescence detector is configured to detect fluorescence at a wavelength in the UV- visible spectrum.

17. The portable mercury detector system as in claim 1 , wherein the fluorescence detector includes a photodiode, photo multiplier tube and/or CCD sensor.

18. The portable mercury detector system as in claim 1 , further comprising a long pass filter positioned between the sample chamber and the fluorescence detector to filter out light at an excitation wavelength of the mercury-binding fluorophore.